Poly-α-olefins (PAOs) are important non-polar lube base stocks with many excellent lubricant properties, including high viscosity index (VI) and low volatility and are available in a wide viscosity range, i.e., a Kv100 of about 2 to about 300 centistokes (cSt)). PAOs are disclosed as lube base stocks, for example, in U.S. Published Patent Application No. 20080177121 A1.
Other important lube base stocks are those derived from one or more Gas-to-Liquids materials (GTLs). GTL materials that are derived via one or more synthesis, combination, transformation, rearrangement, and/or degradation/deconstructive processes from gaseous carbon-containing compounds. GTLs are disclosed as lube base stocks, for example, in U.S. Published Application No. 2007/0265178, which is incorporated herein by reference.
Other important lube base stocks are the Groups I, II, and III base stocks. Groups I, II, and III base stocks are disclosed in “Synthetics, Mineral Oils and Bio-Based Lubricants, Chemistry and Technology” Edited by L. R. Rudnick, published by CRC Press, Taylor & Francis, 2005, which is incorporated herein by reference.
Base stocks of PAOs, GTLs, and Groups I to III exhibit relatively low polarity. This low polarity leads to low solubility and dispersancy for polar additives or sludge generated in lubricants containing PAOs and GTLs.
To compensate for the low polarity of base stocks of PAOs, GTLs, and Groups I to III, lubricant manufacturers commonly incorporate one or more polar co-base stocks. Commonly used co-base stocks are esters or alkylated naphthalenes, which are typically present in the lube base stock at about 1 wt % to about 50 wt % based on the total weight of the base and co-base stocks. Esters and alkylated naphthalenes are disclosed, for example, in U.S. Pat. Nos. 6,627,779 B2 and 6,833,065 B2 as well as WO 03/035585. Other co-base stocks include various dicarboxylic acid esters, which are disclosed, for example, in U.S. Pat. Nos. 2,936,320; 3,251,771; 3,409,553; 4,464,277; and 6,667,285.
It would be desirable to have a polar co-base stock that could be added to non-polar base stocks, such as PAOs, GTLs, and Groups I to III, to improve the solubility of additives and sludge therein.